1. Field of the Invention
The present invention relates to fibre channel networks. More specifically, the present invention relates to methods and apparatus for providing in order delivery of fibre channel frames in a fibre channel network during circumstances such as changes in link state or changes in channel state.
2. Description of Related Art
Many conventional network protocols allow the out of order delivery of a packet sequence. A network node in a TCP/IP based network can receive an out of order set of packets and reorder the packets upon receipt. Packets often arrive out of order if they travel along different paths to reach a destination.
However, some fibre channel devices such as disks, disk arrays, and other storage mechanisms can not handle out of order frames. Link and channel state changes are some of the circumstances that may cause out of order delivery of frames in a fibre channel fabric. Multiple links seen as a single link between two fibre channel entities is referred to herein as a channel. Some mechanisms in existing networks call for the flushing of all frames in the network upon a change in link state. Flushing all of the frames can prevent out of order delivery when paths and routes change in a network. All frames are flushed even if the paths for the frames to the associated destinations are not changed. However, flushing all of the frames either explicitly or implicitly can be very disruptive to network operation, as more frames are dropped than is necessary and network operation is at least temporarily halted.
It is therefore desirable to provide methods and apparatus for improving fibre channel frame delivery and providing in order delivery particularly during link state and channel changes.